Multiple frequency inductive resistivity device

Abstract

In one aspect of the present invention, an induction resistivity tool incorporated into a downhole tool string component comprises an annular radial recess disposed along an outside surface of a tubular wall of the downhole component. At least one electrically insulated induction coil is disposed in the radial recess and adapted to transceive induction signals outward from the tubular wall when carrying an electrical current. The at least one coil is tuned for an optimal signal frequency and an actuator in the downhole component is adapted to put an electrically conductive element into and out of electrical contact with the at least one coil and thereby change the optimal signal frequency.

1. An induction resistivity tool incorporated into a downhole tool string component, comprising:
 an annular radial recess disposed along an outside surface of a tubular wall of the downhole component; 
 at least one electrically insulated induction coil disposed in the radial recess and adapted to transceive induction signals outward from the tubular wall when carrying an electrical current; 
 the at least one coil being tuned for an optimal signal frequency; and 
 an actuator in the downhole component which is adapted to put an electrically conductive element into and out of electrical communication with the at least one coil and thereby change the optimal signal frequency. 
 
     
     
       2. The induction resistivity tool of  claim 1 , wherein the electrically conductive element is a coil tap. 
     
     
       3. The induction resistivity tool of  claim 1 , wherein the electrically conductive element comprises at least one electrically conductive wire, electrically conductive stub, capacitor, inductor, resister, transformer, varicap diode, or combinations thereof. 
     
     
       4. The induction resistivity tool of  claim 1 , wherein the actuator comprises at least one motor, spring, solenoid, transistor, capacitor, varicap diode, inductor, resister, bypass capacitor, decoupling capacitor, multiplexer, or combinations thereof. 
     
     
       5. The induction resistivity tool of  claim 1 , wherein the actuator comprises a switch selected from the group consisting of physical switches, electrical switches, toggle switches, rocker switches, biased switches, trembler switches, pneumatic switches, reed switches, microswitches, centrifugal switches, Hall effect switches, and combinations thereof. 
     
     
       6. The induction resistivity tool of  claim 1 , wherein a plurality of actuators is disposed along the coil and each actuator is adapted to selectively electrically connect and disconnect an electrically conductive element with the coil. 
     
     
       7. The induction resistivity tool of  claim 1 , wherein at least two different electrically conductive elements are actuated by the same actuator. 
     
     
       8. The induction resistivity tool of  claim 1 , wherein the electrical contact of the electrically conductive element with the coil changes a potential electromagnetic circuit path through the coil. 
     
     
       9. The induction resistivity tool of  claim 1 , wherein the optimal signal frequency is adjusted by altering a number of coil turns carrying electrical current. 
     
     
       10. The induction resistivity tool of  claim 1 , wherein a flexible ring of magnetically conducting material is disposed intermediate the coil and a surface of the radial recess and is arranged within the radial recess such that it filters a range of frequencies of the induction signals. 
     
     
       11. The induction resistivity tool of  claim 1 , wherein the coil comprises between 1 and 15 turns of coil. 
     
     
       12. The induction resistivity tool of  claim 1 , wherein the resistivity tool is in communication with a downhole network. 
     
     
       13. The induction resistivity tool of  claim 1 , wherein the coil comprises an electrically insulating coating. 
     
     
       14. The induction resistivity tool of  claim 13 , wherein the electrically insulating coating comprises one or more openings adapted to allow electrical contact between the coil and the electrically conductive element. 
     
     
       15. The induction resistivity tool of  claim 1 , wherein the coil comprises two sets of coil turns, each set adapted to be selectively energized. 
     
     
       16. An induction resistivity tool incorporated into a downhole tool string component, comprising:
 a plurality of annular radial recess disposed along an outside surface of a tubular wall of the downhole component; 
 at least one electrically insulated induction coil disposed in each radial recess and adapted to transceive induction signals when carrying an electrical current; 
 each at least one coil being tuned for an optimal signal frequency; and 
 an actuator in the downhole component which is adapted to put an electrically conductive element into and out of electrical contact with each at least one coil and thereby change their optimal signal frequency. 
 
     
     
       17. The induction resistivity tool of  claim 16 , wherein a plurality of the at least one coils in the same radial recess or in a plurality of radial recesses are each selectively energized. 
     
     
       18. The induction resistivity tool of  claim 16 , wherein at least two of the at least one coils are tuned to the same optimal signal frequency. 
     
     
       19. The induction resistivity tool of  claim 16 , wherein a plurality of the at least one coil in the plurality of radial recesses is each selectively operated at multiple frequencies and adapted to obtain resistivity data from multiple depths of the formation. 
     
     
       20. The induction resistivity tool of  claim 16 , wherein a control signal sent from a control module to the plurality of radial recesses triggers an actuator resulting in changing the optimal signal frequency for at least two coils.